1. Field of the Invention
The present invention relates to a structure for axially supporting a head stack assembly (HSA) with a pivot assembly to support a magnetic head in a magnetic storage device for a computer such as a hard disc drive.
2. Description of the Related Art
A hard disc drive used in a magnetic storage device of a computer needs to be small in size but provided with a high storage capacity. To miniaturize the hard disc drive, reducing the diameter of a magnetic disc is effective and this has actually been practiced by reducing the diameter of the disc from 5 inches to 3.5, 2.5, 1.8, and 1 inch. Along with this, an increase of the storage capacity without changing the magnetic disc diameter is certainly attained.
FIG. 3 schematically shows the internal structure of the hard disc drive. A plurality of magnetic discs D are arranged at equal spacing along a rotary axis C1 being driven rotationally in a unitary manner by a spindle motor (not shown). The writing and reading of data-information to the magnetic disc D is performed by means of a head stack assembly (hereinafter referred also to HSA) 1. The HSA 1 is provided with a plurality of head suspensions 2 supporting a magnetic head (not shown) at their end portion, where it is structured so that a pivot assembly 4 supports an actuator block 3 on which suspension support portions 3a are formed in a plurality of stages to support each of the head suspension 2.
The pivot assembly 4 is disposed along a rotary axis C2 parallel to the rotary axis C1, and a shaft 5 is inserted into a central portion thereof. In addition, the pivot assembly is provided with a sleeve 6 supported on the shaft 5 through a bearing. Since the actuator block 3 is fixed to the sleeve 6, it is possible to swing each head suspension 2 around the rotary axis C2 together.
Furthermore, although not shown, a coil is provided at an end portion 3b opposite to the head suspensions 2 across the rotary axis C2, and magnets are arranged on both sides of the coil to thereby form a voice coil motor. The HSA1 is rotated around the rotary axis C2 by exciting the voice coil motor, and thus the magnetic head can be moved to a demanded position of the magnetic disc D.
To increase storage capacity on individual disc, the narrowing of tracks for writing and reading the data-information is necessary, where on the other hand it is inevitable to maintain the coaxiality of the pivot assembly 4 and the actuator block 3 highly precise to accurately trace the head for writing and reading on the narrow track.
FIGS. 4A and 4B show a conventional fitted portion between the actuator block 3 and the pivot assembly 4. FIG. 4A is a cross-section in the direction perpendicular to the shaft, and FIG. 4B is a cross-section in the axial direction. The fixation of the actuator block 3 to the pivot assembly 4 has been conventionally performed by adhesion. However, since this method of fixing with an adhesive requires an adhesive layer 8 is kept between the actuator block 3 and the sleeve 6 of the pivot assembly 4, it is inevitable to make large clearance (the difference in dimension) between the inner diameter of the actuator block 3 and the outer diameter of the sleeve 6. In addition, if the thickness of the adhesive layer is unequal (keeping equal thickness it is very difficult), the amount of the shrinkage of the adhesive layer 8 is different in each area, which would easily induce a large eccentricity. Moreover, it is difficult to settle direction of eccentricity once such an eccentricity occurs. Furthermore, using thermo-setting adhesive would involve a lot of factors making a precise control of coaxiality between pivot assembly 4 and actuator block 3 difficult. One of those factors is that the clearance between pivot assembly 4 and sleeve 6 of actuator block 3 differs before and after heating. In addition, a lot of problems in relation to the adhesion would be involved which are for example an absolute necessity of cleaning the adhering surface prior to adhesion, or no possibility of disassembly and rework after adhesion. Disassembly and rework after adhesion would be impossible.
The present invention has been made in view of the aforementioned aspects and its object is to facilitate the fixation of the pivot assembly to the actuator block and to obtain the stable coaxiality of the actuator block and the pivot assembly.
According to a first aspect of the present invention, an actuator block supported by a pivot assembly is characterized in that a screw hole passing through from the outside is provided in a fitting hole into which the pivot assembly is to be inserted, and contact portions between a sleeve of the pivot assembly and the fitting hole are formed at a predetermined distance in a circumferential direction respective to the screw hole.
According to the present invention, a screw is screwed into the screw hole so that the sleeve of the pivot assembly fitted into the fitting hole is pressed by the end portion of the screw. Thus, the sleeve of the pivot assembly is fixed by being clamped between the end portion of the screw and the contact portions in the interior of the fitting hole. At this moment, the pivot assembly becomes eccentric to the fitting hole, but the direction of the eccentricity is fixed. The degree of the eccentricity can be held to a minimum since the dimensional difference between the fitting hole and the sleeve of the pivot assembly can be kept to the minimum as long as the fitting process is not affected.
The actuator block according to a second aspect of the present invention is provided with contact portions at two areas. According to the present invention, the sleeve can be fixed at three areas, i.e., the two contact portions and the end portion of the screw.
The actuator block according to a third aspect of the present invention is characterized in that the contact portions are arranged by forming a non-contact surface against the sleeve in the predetermined area of the fitting hole, the area opposite to the screw hole across a center axis. In the present invention, the non-contact surface against the sleeve is arranged in the predetermined area of the fitting hole so that the end portions of the non-contact surface inevitably contact with the sleeve to form the contact portions.
The actuator block according to a fourth aspect of the present invention is characterized in that the contact portions are arranged by forming a non-contact surface against the fitting hole on the predetermined area of the sleeve, the area opposing a position confronting a screw hole provided in the fitting hole across a center axis. In the present invention, the non-contact surface against the fitting hole is arranged in the predetermined position of the sleeve so that the end portions of the non-contact surface inevitably contact with the fitting hole to form the contact portions.
The actuator block according to a fifth aspect of the present invention is characterized in that the sleeve is securely fixed by making the end of the screw screwed through the screw hole abut to a plain surface which is formed on the sleeve.
The actuator block according to a sixth aspect of the present invention is characterized in that the screw to be screwed into the screw hole is a set screw. The use of the set screw prevents an unnecessary protuberance to the outside of the actuator block.